Centrifugal casting mold



Aug. 17, 1937. H, c, FRET; 2,090,289

CENTR IFUGAL GAS TING MOLD Filed June 12, 1954 m ,3 INVENT ll/LLARD C. F.72

ATTORN EY "Patented Aug. 17, 1937 UNITED STATES "PATENT" OFFICECENTRIFUGAL CASTING MOLD Hillard C. Fretz, Kokomo, Ind., assignor, bymesne assignments, to Union Carbide and Carbon Corporation, acorporation of New York Application June 12, 1934, Serial No. 730,197

. 7 Claims. (01. 22-45) This invention relates to centrifugal castingmolds. having for its object the provision of atures tend to freeze soquickly when the source- '-of heat is removed that the time requiredfortransferring the molten material from the crucible into the castingcavities of the mold is an element of primary importance. To assist inminimizing this time, use is made of centrifugal force to create apressure on the molten material and force it intothe casting cavity. Igo Heretofore, the casting cavities in centrifugal casting molds haveextended substantially radially outward from the central opening orsprue. In such molds the centrifugal force is not fully developed untilthe molten material in the sprue :5 is rotating at the same speed as themold, so that there is an appreciable interval of time before thecasting cavities are entirely filled. Furthermore, the inertia of themolten material before it is rotating at the same speed as the mold socauses the casting cavities to fill along their backedges first.Consequently, the castings produced often have defective surfacescontaining ridges and pits formed by uneven flow of materia landstep-wise solidification. This is especially true so when castingcertain alloys high in tungsten, such as those having a composition of:

Tungsten 70 to 95% Carbon... 0.5 to 6% 40 Other metals ...5 up to 25%angular accelerating force are effectively utilized; to exert a pressureon this material and to force it into the casting cavities duringrotation of the mold. The exact manner-in which this is accomplishedwill be evident from the following description taken in conjunction withthe accompanying drawing, in which:

"5 Figure 1 is a plan view of one section of a preferred form of mold inaccordance with this invention;

Figure 2 is'a cross-sectional view of the assem bled mold on the line 22 of Fig. 1; and

Figure 3 is a broken cross-sectional view on the line 3' 3 of Figure 1.p

Referring to the drawing, the mold may compn'se two annular members I 0and II separated by a spacer plate l2. The material of which the mold ismade may be any suitable material re-" sistant to high temperature heat,for example, a graphite composition. The parts of the mold are heldtogether by any suitable means, such as a clamp or moldholder, which mayalso conveniently serve as a means of attachment to a. power shaft forrotating the mold. Each oi the annular members or sections is'providedwith a plurality of recesses l3 spaced about and communi cating with acentral opening or'sprue It. The recesses of each member may bevertically staggered with respect to the recesses of the adjoiningmember, so that a recess in the upper member ill occupies a positionintermediate two recesses of the lower member I l, as indicated by thedotted lines in Figure 1. There is then produced a staggered flow ofmolten material from the sprue it into the recesses 13. Theopen sides ofthe recesses l3 are closed in the assembled mold by the spacer plate l2so as to form a plurality of outwardly extending pockets or castingcavities.

'These cavities extend rearwardly with respect to the direction ofrotation of the mold as indicated by the curved arrow in Figure 1, sothat the lagging angle between the longitudinal axis of each recess andthe radius of the sprue to the mouth of the recess is between 90 and 170degrees. This lagging angle is indicated by the angle a-between the axisa: and the radius r in Figure 1. In a preferred embodiment, the outeredge of each of the recesses I3 is substantially tangential to theperiphery of the central sprue ll. The entrance IE to the central sprueI4 is preferably constricted or necked as indicated in Figure 2 to avoidspattering of the molten material and to facilitate curved arrow inFigure 1, the rotating speed varying with the type of material to becast, the

size and shape of the castings, the diameter of the mold, and theviscosity of the molten material. For alloys high in tungsten of thetype previously indicated, a speed of 1725 revolutions per minute and amold six inches in'diameter have been found to be satisfactory. Themolten material is then poured into the sprue. Until this materialbegins to rotate with the mold, no centrifugal force is exerted thereon;the force is entirely an angular accelerating force which acts on thematerial in a direction tangential to the direction of rotation. As thematerial increases its rotational speed, the centrifugal force increasesand the angular accelerating force decreases until, when the moltenmaterial is rotating at the same constant speed as the mold, the forceis entirely centrifugal. It will thus be readily appreciated that use ismade of both of these forces to press the mo1ten-- material into thecasting cavities of a mold constructed in accordance with the presentinvention.

A further advantage of the form of mold shown in Figure l is that, for agiven width of the casting cavity, the mouth of the cavity exposed tothe sprue is wider, which further facilitates the entrance of the moltenmaterial into the cavity. These features considerably shorten the timerequired for filling the casting cavities. Furthermore, the materialenters the cavity in a straight line approximately parallel to the axisof the cavity, so that the cavity is filled rapidly from the bottom up.The result is to produce an improved casting which is substantially freefrom flow lines, ridges, pits, and other defects.

It is contemplated that variations and modifications of the particularmold shown and described herein. may be made without departing from thescope of this invention. The mold may have only a single set of castingcavities, in which case the spacer plate is eliminated and the upperelement contains no recesses but serves to close the open side of therecesses in the lower element. Also, it is possible to have more thantwosets of casting cavities, in which case one or more of the elementsmay be provided with recesses on both sides thereof. The length, width,depth, shape, and cross-section of the casting cavities may vary inaccordance with the type and shape of the castings desired, the cavities45 being in all cases so disposed that both the centrifugal force andthe angular accelerating force are effectively utilized to force themolten material into the casting cavities during rotation of the mold.It is possible to increase the num- 50 her of cavities in a mold of anygiven size by decreasing the size of the mouth of each cavity. These andother variations and modifications are clearly within the scope of thepresent invention, and I do not wish to be limited to 55 or by thespecific embodiments shown herein by 65 having an axially disposedcircular sprue and a plurality of outwardly and rearwardly extendingnonradial mold cavities opening directly into said sprue and havingtheirouter ends closed, said annular body being of material resistant to70 high temperature heat, the longitudinal axis of each of said cavitiesbeing a substantially straight line forming with the radius of said bodyto the mouth of the cavity a lagging angle between 90 and 170 degrees,whereby the angular accelerat- 75 ing force and the centrifugal forceare both efally disposed circular sprue and a plurality of 10 outwardlyextending molding cavities spaced about and opening directly into saidsprue, the outer edges of said cavities being substantially tangentialto the periphery of said sprue.

3. A centrifugal casting mold for high tem- 15 perature meltingmaterials comprising a plurality of cooperating annular members havingannular spacer plates therebetween, said annular members and spacerplates being of material resistant to high temperature heat, each of 20said annular members having a central sprue opening cooperating with a.similar opening in said spacer plates and a plurality of recesses spacedabout and communicating with said sprue so as to form by cooperationwith said spacer 25 plates a plurality of outwardly extending cavities,the angle at which said cavities extend outwardly from said sprue beingsuch that the angular accelerating force as well as the centrifugal\force is efiectively utilized during rotation of said mold to force themolten material into said cavities and to maintain said materialtherein.

4. A centrifugal casting mold for high tem-" perature melting pointmaterials containing tungsten, comprising a plurality of cooperatingrefractory annular members having annular refractory spacer platestherebetween, each of said members having a. concentric axially disposedcircular sprue opening cooperating with a similar opening in said spacerplates and a plurality of recesses spaced about and communicating withsaid sprue so as to form by cooperation .with said spacer plates aplurality of outwardly extending cavities, the outer edges 01 saidcavities being substantially tangential to the periphery of 5 saidopening.

' 5. A centrifugal casting mold for high temperature melting materialscontaining tungsten carbide, comprising a plurality of cooperatingannular members having annular spacer plates therebetween, said annularmembers and spacer plates being of material resistant to hightemperature heat, each of said annular members having a central sprueopening cooperating with a similar opening in said spacer plates and aplurality ofv recesses spaced about and communieating with said sprueopening so as to form by cooperation with said spacer plates a pluralityof outwardly extending cavities, the recesses of each of said annularmembers being vertically staggered with respect to the recesses of anadjacent annular member, and the angle at which said cavities extendoutwardly from said sprue being such that the angular accelerating forceas well as the centrifugal force is efiectively utilized during rotationof said mold to force the molten material into said cavities and tomaintain said material therein. I

6. A centrifugal casting mold for high'temperature melting materialscomprising a plural- 79 ity of cooperating annular members having one ormore annular spacer plates therebetween, said annular members andspacer, plates being of ma.- terial resistant to high temperature heat,each of said annular members having a central sprue perature heat, saidbody having an axially disposed circular sprue and a plurality ofoutwardly extending non-radial cavities having their inner ends openingdirectly into said sprue and their outer ends closed, the longitudinalaxis of each 5 cavity being substantially parallel to a tangent to theperiphery of said sprue adjacent the inlet of such cavity.

I-JILLARD C. FRE'I'Z.

